As a door opening and closing device for facilitating opening and closing of a door, the applicant has proposed a door opening and closing device illustrated in FIG. 16 (refer to Patent Literature 1). As illustrated in FIG. 16, a door 2 is connected to a housing 1 via hinges 3 to be pivotable about a horizontal axis. The closer the opening angle of the door 2 gets to 90 degrees, the greater the moment produced by own weight of the door 2 becomes, and this requires a greater force to open the door 2. The door opening and closing device 4 exerts a force for assisting opening and closing of the door 2 so as to facilitate manual operations of opening and closing of the door.
The door opening and closing device 4 includes a main opening and closing device body 5 attached to the housing 1 and an arm 6 pivotably provided to the main opening and closing device body 5. At a tip end of the arm 6, an arm slider 7 is provided to be slidable in a length direction of the arm 6. The arm slider 7 is pivotably linked to the door 2. Inside the main opening and closing device body 5, a slider crank mechanism (not shown) for exerting a force to assist opening and closing of the door 2 is provided. The force for assisting the opening and closing of the door 2 is transmitted to the arm 6 from the slider crank mechanism.